1. Field of the Invention
This invention relates to a catalytic aliphatic carbonate process which comprises contacting an alcohol, carbon monoxide, a Bronsted base, a Group VIIIB element selected from ruthenium, rhodium, palladium, osmium, iridium or platinum, oxygen and a redox co-catalyst.
2. Description of the Prior Art
Mador et al., in U.S. Pat. No. 3,114,762, issued Dec. 17, 1963, describes the preparation of aliphatic carbonates by the reaction of aliphatic alcohols with carbon monoxide carried out in the presence of a salt of palladium or platinum metal. Mador's process produces undesirable by-products including ethers and alkyl halides. Mador's patent fails to describe the use of oxygen as an essential catalyst process component in an aliphatic carbonate process in order to avoid the formation of undesirable ether and/or alkyl halide by-products.
M. Graziani et al., Journal of Organometallic Chemistry, Vol. 27 (1971), pages 275-278, describes the preparation of diethyl carbonate, ethyl chlorocarbonate, ethyl acetate and unknown reaction products--where reaction products vary in accordance with the reactants used by Graziani and the order of addition of the reactants to the reaction environment. Graziani fails to describe the use of oxygen as an essential ingredient in a reaction route leading to the formation of ethyl carbonate in order to avoid the formation of undesirable ethyl chlorocarbonate, ethyl acetate, and an unidentified reaction product.
Perrotti et al. in U.S. Pat. No. 3,846,468, issued Nov. 5, 1974, later reissued as U.S. Pat. No. Re. 29,338 on Aug. 2, 1977 describes the preparation of carbonic acid esters by the stoichiometric reaction of an aliphatic alcohol with carbon monoxide and oxygen carried out in the presence of copper complexed with a Lewis base, i.e. an electron donor species, e.g. pyridine, dipyridyl, imidazole, phenanthroline, alkyl or aryl phosphines, dimethylsulfoxide, dimethylformamide, quinuclidine, CH.sub.3 CN, C.sub.6 H.sub.5 CN, malonitrile, succinodinitrile, adiponitrile, etc. Perrotti's Lewis bases function as electron donor species which basic species form complexes with the metals (M) of the IB, IIB, and VIII of the periodic system. When Perrotti's Lewis base species are substituted for the Bronsted bases in my process Perrotti's Lewis bases--as suggested by Perrotti--coordinate with my Group VIIIB elements with the result that no aliphatic carbonate is formed. Wherein Bronsted bases are defined herein and in the appended claims the use of the term "Bronsted base" is intended to expressly exclude the use of Perrotti's Lewis bases within the scope of my process. Carbon monoxide--not functional as a Lewis base in my process--is of course included as a reactant in my process. Perrotti's process requires the sequential addition of oxygen followed by carbon monoxide.
Unexpectedly, I have found that aliphatic carbonates can be formed in a catalytic process when alcohols are carbonylated in the presence of oxygen and a Bronsted base, i.e. a proton acceptor species, e.g. sodium hydroxide, sodium methoxide, triethylamine, dioctylbenzylamine, 1,2,2,6,6-pentamethylpiperadine, etc. My Bronsted bases function as a proton acceptor species, i.e. basic species which do not form complexes with the VIIIB elements employed in my process. Accordingly, wherein Bronsted bases as defined herein are used in my process it is to be understood that my Bronsted bases do not form legand complexes with my VIIIB elements and--in contradistinction to Perotti--function as proton acceptors of hydrogen derived from the alcohol reactant. My catalytic process provides aliphatic carbonates while avoiding the formation of undesirable by-products, e.g. alkyl halides, ethers, esters, etc., without requiring the sequential addition of reactants, e.g. oxygen and carbon monoxide, as described by Perrotti.